On Sat, Mar 16, 2024 at 10:17:00AM +0800, lixianglai wrote:
> Hi Gerd:
> > On Mon, Mar 11, 2024 at 02:39:31AM -0700, Chao Li wrote:
> >> This library for PEI phase, and obtains the QemuFwCfg base address by
> >> directly parsing the FDT, reads and writes the data in QemuFwCfg by
> >> operating on the QemuFwCfg base address.
> >>  create mode 100644 
> >> OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/FdtQemuFwCfgPeiLib.c
> >>  create mode 100644 
> >> OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/FdtQemuFwCfgPeiLib.inf
> >>  create mode 100644 
> >> OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/QemuFwCfgLibInternal.h
> >>  create mode 100644 
> >> OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/QemuFwCfgPei.c
> > Is there anything LoongArch-specific in there?
> No,The main function of this lib library is to obtain the fwcfg base address 
> by parsing fdt in the pei stage,
>  and provide access to fwcfg through mmio mode,
>  the difference between it and the existing library is that the fwcfg base 
> address is not hard-coded in the compilation stage,
>  and is accessed through mmio rather than io port.

That would be the case for risc-v and aarch64 too, although I think they
don't need fw_cfg right now (they get all info needed via fdt).

I think we should add this as OvmfPkg/Library/FdtQemuFwCfgLib.

> Another point that needs to be explained is that because loongarch virtual 
> machine runs on flash in pei phase,
> it cannot assign the pcd global variable, so we use Hob as the global 
> variable to store the fwcfg base address.

I think the dynamic PCD database is stored in a HOB and you should be
able to set PCDs them even when running from (read-only) flash.

take care,
  Gerd



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